Reaction Steps
Piperidine (0.39 mL, 4.0 mmol) was added to a suspension of 3,4-dihydroxybenzaldehyde (0.55 g, 4.0 mmol) and 2-[(carboxyacetyl)amino]benzoic acid (0.74 g, 3.3 mmol) in toluene (5.0 mL) and treated according to Procedure 2, acidifying with 1 M HCl. (E)-2-[[3-(3,4-Dihydroxyphenyl)-1-oxo-2-propenyl]amino]benzoic acid (0.82 g, 83%) was obtained as a brown crystalline solid; mp 204-206° C.; lit. [24] 204-206° C.; δH (500 MHz, DMSO-d6) 6.50 (d, J=15.5 Hz, 1H, CH═CHCO), 6.77 (d, J5′,6′=8.0 Hz, 1H, H5′), 7.00 (dd, J5′,6′=8.0, =2.0 Hz, 1H, H6′), 7.08 (d, J2′,6′=2.0 Hz, 1H, H2′), 7.14 (t, J3,4=J4,5=8.0 Hz, 1H, H4), 7.44 (d, J=15.5 Hz, 1H, CH═CHCO), 7.61 (td, J4,5=J5,6=8.0, J3,5=1.5 Hz, 1H, H5), 8.00 (dd, J3,4=8.0, J3,5=1.5 Hz, 1H, H3), 8.58 (d, J5,6=8.0 Hz, 1H, H6), 9.11 (s, 1H, OH), 9.52 (s, 1H, OH), 11.25 (s, 1H, NH).
